Process for formation of coating film on plastic material and coated article

A process for formation of a coating film on a plastic material, which comprises the steps of:

• coating the plastic material with an aqueous primer coating composition;
• and thereafter drying the resultant primer coating film in such a manner that its nonvolatile content will not be less than 70 weight %;
• and thereafter overcoating the primer coating film with an aqueous base paint composition;
• and thereafter drying the resultant base coating film in such a manner that its nonvolatile content will not be less than 60 weight %;
• and thereafter overcoating the base coating film with a two-component clear paint;
• and thereafter baking the resultant three-layered coating film onto the plastic material;
• with the process being characterized in that:
• the aqueous base paint composition includes:
• an emulsion resin (a) as obtained by carrying out emulsion polymerization of an α,β-ethylenically unsaturated monomer mixture having a nonvolatile acid value of 3 to 50 mgKOH/g;
• a water-soluble (meth)acrylic resin (b) having a nonvolatile acid value of 110 to 200 mgKOH/g;
• and a polyether-modified carbodiimide (c);
• wherein the α,β-ethylenically unsaturated monomer mixture includes a (meth)acrylate ester in an amount of not smaller than 65 weight % wherein the (meth)acrylate ester has an ester portion containing 1 or 2 carbon atoms;
• and wherein:
• the nonvolatile content of the (a) is in the range of 55 to 75 weight %, that of the (b) is in the range of 0.5 to 15 weight %, and that of the (c) is in the range of 15 to 44.5 weight %, relative to the total nonvolatile content of the (a) to (c);
• and
• the aqueous primer coating composition includes an acid-anhydride-modified chlorinated polyolefin emulsion resin (A), an aqueous urethane dispersion (B), an aqueous epoxy resin (C), and an organic strong base and/or its salt (D), wherein:
• the nonvolatile content of the (A) is in the range of 20 to 60 weight %, that of the (B) is in the range of 10 to 40 weight %, that of the (C) is in the range of 20 to 60 weight %, and the (D) is in the range of 1 to 5 weight % relative to the total nonvolatile content of the (A), (B), and (C).